The fruits of genius

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Isaac Newton is incredibly important today for several reasons. For one thing, he's a great heroic icon of science. The only thing that most people know about Isaac Newton is that supposedly he watched an apple fall from a tree and conceived the theory of gravity. That story may or may not be true, but it's one that he promoted in the few years shortly before he died (he told it to four different friends). It's become a foundational myth of scientific discovery, rather like Archimedes jumping out of his bath shouting ‘Eureka!’ It conveys the idea that there's some very gifted people whom we now call scientific geniuses who have a special access to the truth.

Isaac Newton, in a way, has become a secular saint for our society, rather like Catherine is known by her wheel or St. Jerome by his lion. Isaac Newton is a secular saint and his attribute is his apple.

The Principia Mathematica

In terms of his scientific work, Newton’s most important, long lasting book is the Principia Mathematica or The Mathematical Principles of Natural Philosophy. It's still important because it contains all the basic rules of physics that we still employ for life on Earth and out in space, although it's not very helpful for the subatomic world of quantum physics. But for ordinary life – even for building a spaceship – Newtonian physics is what we still use.

He summarised his thinking in his major work, Principia Mathematica, which is not written in calculus. He used the language of geometry because he believed that that was the great language of the Greeks, and that nothing had surpassed it.

There are several aspects to the Principia. He starts by laying down the basic laws of mechanics. There are three basic laws which we still use in the most elementary calculations. The most important is the third, which introduces a new entity: force, which is mass times acceleration.

In terms of astronomy, the most important aspect of the Principia is showing that comets go around the sun in ellipses, just like planets. There's only one big fold-out diagram in his book and that shows a picture of the sun and then a diagram of a comet that went round the back of the sun and came out the other side again. Before then, the most popular theory was that comets, planets and indeed the universe were all held together by magnetism. But by observing the comet, Newton proved that it didn't go towards the sun and bounce back again. On the contrary, it went round the back just like a planet.

Two revolutionary ideas

The first revolutionary idea in the Principia was to show that the same laws exist on Earth as throughout the rest of the universe. Before then, dating back to the Greeks and Aristotle, the universe was divided into two basic zones. There was what happened up in the heavens, where all was perfection and order because that was God's realm. Everything moved in circles and there was a single, very fine spiritual ether that pervaded what we now think of as empty space. Down on earth, the laws of nature were very different. There were only four elements – earth, air, fire and water – and everything was movement, corruption and degeneration.

So there were two distinct spheres of the universe. Building on a couple of hundred years of research, Newton contradicted that by saying, no, there is just one law that governs the universe. The force that makes an apple fall to the ground from its tree is the same force that makes the earth go round the sun.

The second revolutionary aspect of Newton's Principia was that he made the universe mathematical. That, I think, was the most fundamental change. He introduced the idea that you can express everything quantitatively. You can set up equations to describe not only the way that the planets go around the sun but also the way that living beings operate and human systems work. This fundamentally quantitative approach to the universe is something that we still have and it's very much Newtonian.

Counting the colours in the rainbow

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Newton’s book on gravity isn't the only reason he's famous. If you look at his monument in Westminster Abbey, you can see that he's reclining like a Roman, with his elbow leaning on four books. One of those works is the Principia, his book about maths and natural philosophy. The second book is about optics, which is his most important and enduring scientific legacy.

Most of Opticks is about optical experiments, the most famous of which is about putting seven colours in the rainbow. That’s quite a complicated story, because whether there are seven colours in the rainbow is to some extent arbitrary. If you look at medieval manuscripts depicting the rainbow that signalled to Noah that it was safe to come out because the flood had receded, you can see that other people thought the rainbow had three colours. When Newton looked at the spectrum of colours in the rainbow, he didn't immediately see seven colours; at first, he saw five. The reason he divided the spectrum into seven colours is because he believed in universal harmony.

Newton’s sloppy clockmaker

In many ways, Newton's view of the universe was completely different from ours. He's often credited with eliminating God, but that's completely wrong. He was a deeply religious man. God was crucial for him. For Newton, the whole point of studying nature was to get closer to God.

He believed in a universe that was alchemical and alive. His alchemical studies weren't just eccentric experiments carried out by someone who was reclusive and a bit mad. They were central to some of the theories he had about natural philosophy. He suggested that in this living universe, God intervenes from time to time, sending a comet with live vegetative matter in its tail to somehow restore the equilibrium of the earth.

That’s something he was much criticised for. His great rival, Gottfried Leibniz, who competed with Newton to be recognised as the inventor of calculus, dismissed Newton’s notion of God. He thought it was as though Newton's God were a sloppy clockmaker, who couldn't wind up his clock at the beginning of the universe and set it going. He has to keep winding it up from time to time. So, our version of Newton is rather different from the one that Newton himself put forward.

An eclectic range of interests

Going back to Newton's monument in Westminster Abbey, he's reclining his elbow on four books – one on gravity, another on optics and another two on theology and ancient chronology that we don’t know much about now.

Because the world has become so scientific, we tend to focus on the parts of Newton's work that seem important to us. But as far as he and his contemporaries were concerned, his other areas of scholarship were just as important. In theology, for instance, he owned about 30 Bibles, one of which still exists in the university library at Cambridge. You can see by the way the pages are thumbed and dog-eared that his favourite book was the Book of Daniel.

He wrote a lot about theology, biblical interpretation and King Solomon's temple. And he also wrote about what he called ancient chronology: the idea of redating ancient kingdoms such as those of the Egyptians and the Babylonians. You can do that through astronomy: just as Newton could use astronomy to predict an event in the future, he could use the same theory to work out exactly when an eclipse or some other sort of astronomical event happened in the past.

From mathematician to millionaire

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Newton was president of the Royal Society of London, so in that sense, he was a very important scientific figurehead who liaised with other experimenters all over Europe. That was a very important part of his work. He was also Master of the Royal Mint, which makes all of England's coins. That position at the time was roughly equivalent to being the governor of the Bank of England now. So Isaac Newton was making a lot of decisions that affected Britain's economic situation.

Newton invested in the stock market, and in particular, global trading companies like the East India Company, which sent ships overseas and which profited from the international slave trade. There's no evidence that Newton himself was directly involved in the slave trade. On the other hand, like many people in Britain, he benefited from it financially because the whole English economy depended on global trade. He benefited from it personally because his role as the head of the Mint of England was to ensure that we got the lowest prices possible for African gold dug up by African slaves, whose families were being sent over to America as captives. He also personally made a profit because for every gold coin that was minted, he received a fee. He became very rich and died a wealthy man. He had 30,000 pounds, which is worth millions in today's money.

Discover more about

Isaac Newton and his scientific legacy

Fara, P. (2021). Life After Gravity: Isaac Newton's London Career. Oxford University Press.

Fara, P. (2002). Newton: The Making of Genius. Macmillan.

Fara, P. (2010). Science: A Four Thousand Year History. Oxford University Press.

Isaac Newton, a man of science and religion